Complex manufacturing operations often employ multiple operating stations or cells in which sequential machining, assembly or other operations are performed on a workpiece. These sequential operations are often controlled by a PLC (Programmable Logic Controller) in order to automate work station operations and material flow. PLCs are industrial computer control systems that continuously monitor the state of input devices and make decisions based on custom software to control the state of output devices. Broadly, PLCs comprise a central processing unit (CPU), a memory system, input modules and output modules, a programming device and one or more operating modules that allow an operator to process information to be displayed and new control parameters to be entered.
PLCs typically perform four sets of operations: scanning the state of input devices, executing user created program logic, controlling output devices connected to the PLC and performing miscellaneous housekeeping activities which may include communications with programming terminals, internal diagnostics, etc. Several languages are employed to program PLC'S, although ladder logic is most commonly used. More recent PLC applications may utilize simulation software programs which allow simulation of a variety of operating conditions useful in designing and testing the PLC system. As a result, in part, of the development of simulation programs, a number of “virtual” relationships are established between tooling, control devices, PLC logic, PLC I/O fault bits, etc.
Complex manufacturing systems controlled by PLC's sometimes experience failures which are registered as a machine fault condition, or a “fault”. A fault exists where, as a result of the PLC executing the PLC logic used to control the operating cycle of tooling, the PLC has encountered a set of conditions that indicate a non-manual intervened interruption has occurred, causing the system to stop production. Such faults may be due to the failure of a physical device, such as a sensor within the system, or may be caused by an error in software logic or other non-physical phenomena.
In the past, a machine fault was communicated to an operator by means of a fault code or textual machine fault message being displayed on a graphical display, typically a touch screen display in view of an operator. These fault codes and textual messages were normally brief, and even cryptic, providing little information concerning the exact nature and location of the problem giving rise to the fault. Because of the highly abbreviated nature of these fault messages, an experienced operator was required to interpret the intent of the message. Typically, the fault message provided only a PLC I/O memory bit address corresponding to an element that was bad, without any reference to the physical location of the fault within the manufacturing system, or identification of the particular control device type.
A number of virtual relationships have been established between various parts of the PLC based system but these relationships have not been advantageously used in diagnosing faults. For example, existing PLC control logic simulation includes the use of: PLC control logic that is used on the manufacturing plant floor; virtual tooling models that interact with the execution of the PLC logic during a simulation; virtual control devices such as sensors and actuators; 3 D visualization data of the tooling, facilities and control devices. When setting up the PLC control logic simulation “virtual wire” connections are made between the pertinent PLC I/O locations and the virtual control devices, exactly replicating the relationship between the physical tooling and PLC hardware and logic. PLC control logic simulation (virtual PLC) is performed where the PLC logic is tested against the virtual tooling and control device models. The end result is PLC logic that is verified to process design intent. In the past, the verified PLC logic files are the only information sent down stream in the process of building tools for use in tool tryout and production from the control logic simulation process.
The inability to quickly identify, recognize and locate devices within the manufacturing system responsible for faults increases system downtime and impairs timing of launch ramp up of new PLC based manufacturing systems.
Accordingly, there is a need in the art for an improved system for rapidly identifying and visualizing faults in PLC-based manufacturing Systems which overcomes the problems discussed above. The present invention is intended to satisfy this need.